Light-absorbing dyes incorporated in silver halide photographic materials can accomplish a variety of goals, including their use as filter dyes, acutance dyes or anti-halation dyes.
When present in a non-photosensitive top layer or intermediate layer they typically serve as filter dyes eliminating an unwanted part of the light spectrum of the exposure source. A well-known example is the yellow filter layer usually present in colour photographic materials in order to prevent blue light from reaching the green sensitive and red sensitive layers. Another example is formed by UV-absorbing compounds, usually present in the top protective layer, which prevent photochemical deterioration of the image dyes formed by colour development. Examples of useful UV-absorbers include the cyanomethyl sulfone-derived merocyanines of U.S. Pat. No. 3,723,154, the thiazolidones, benzotriazoles and thiazolothiazoles of U.S. Pat. Nos. 2,739,888, 3,253,921, 3,250,617 and 2,739,971, the triazoles of U.S. Pat. No. 3,004,869, and the hemioxonols of U.S. Pat. No. 3,125,597.
On the other hand light-absorbing dyes when present in the emulsion layer can serve as so-called "acutance dyes" or "screening dyes" improving the image sharpness by reducing the sidewise scattering of light by the emulsion grains.
In a third application light-absorbing dyes act as "anti-halation dyes" improving the image sharpness by diminishing the upward reflection of light by the support into the emulsion layer. For this purpose the dye can be incorporated in an undercoat, being a non-photosensitive layer between the emulsion layer and the support, or it can be incorporated in the base itself, or preferably, it can be present in one or more backing layers of the photographic material.
Useful dyes absorbing in the visible spectral region include, for instance, the coloured pigments of U.S. Pat. No. 2,697,037, the pyrazolone oxonol dyes of U.S. Pat. No. 2,274,782, the styryl and butadienyl dyes of U.S. Pat. No. 3,423,207, the diaryl azo dyes of U.S. Pat. No. 2,956,879, the merocyanine dyes of U.S. Pat. No. 2,527,583, the merocyanine and oxonol dyes of U.S. Pat. Nos. 3,486,897, 3,652,284 and 3,718,472, and the enaminohemioxonol dyes of U.S. Pat. No. 3,976,661. Absorbing dyes can be added as particulate dispersions as disclosed in U.S. Pat. No. 4,092,168, EP 0 274 723 and EP 0 299 435.
Infra-red absorbing dyes are described in EP 0 251 282, in EP 0 288 076, and in U.S. Pat. No. 4,839,265.
Dyes absorbing in the red spectral region of the di- or triphenylmethane type, some of which bear an electron-withdrawing group, are disclosed in e.g. GB 769,749, U.S. Pat. No. 2,282,890, DE 1,038,395, FR 2,234,585, JP-A-59-228250, U.S. Pat. No. 2,252,052 and A. Guyot, Compt.Rend. Vol. 114 (1907) p. 1120. Some of the compounds disclosed contain one or more water-solubilizing groups.
Light-absorbing dyes must fulfill a number of strict requirements. They should wash-out or decolourize as completely as possible during photographic processing in order to minimize unwanted residual dye stain. When washed-out they or their reaction products should not deteriorate the physical or sensitometric properties of the photographic material during prolonged continuous processing. Moreover, in order to be effective during exposure, the spectral characteristics of incorporated anti-halation dyes or acutance dyes should match as good as possible the spectral sensitivity distribution of the emulsion layer. In its turn this spectral sensitivity distribution has to be tuned to the spectral characteristic of the exposure source.
In recent years new techniques of image recording have emerged wherein the exposure source of the recording apparatus is a laser unit. For instance, one application of lasers as exposure units is situated in the field of radiographic monitoring photography where a hard copy of radiographic information has to be produced. Other applications are situated in the pre-press field of phototype-setting and image-setting, where recorders are marketed which employ Ar ion lasers, He-Ne lasers or solid state semiconductor lasers, also called laserdiodes, as exposure source. The latter type of laser, the laserdiode, shows some advantages compared to other laser types such as low cost price, small size, long life time and no need for an acoustic-optical modulator. Generally the emission wavelength of these semiconductor laser beams is longer than 700 nm and mostly longer than 750 nm. So photographic materials appropriate for exposure by devices employing such laserdiodes must be sensitized for the near infra-red region of the radiation spectrum. Suitable photographic materials to be used with semiconductor laser device are disclosed in Japanese Unexamined Patent Publication (Kokai) No 61752/85 and U.S. Pat. No. 4,784,933. Commercial infra-red sensitized film and paper were announced by Eastman Kodak Co in "Proceedings Lasers in Graphics, Electronic Publishing in the '80's, Vol 2 (September 1985) p. 508, and put on the market lateron. Other manufacturers followed including Agfa-Gevaert N.V. and Fuji Photo Film Co. An example of an image-setter using a laserdiode exposure is the PROSET 9800 apparatus marketed by Miles Inc., Agfa division.
One problem in the field of imaging by laserdiodes emitting in the near infra-red is the rather high required sensitivity level of the infra-red sensitized photographic material due to the low energy output of this laserdiode type which is in the order of a few milli-Watts. A second problem consists in the usually poor storage quality of emulsions sensitized with long-chain cyanine dyes. Moreover, technicians supplying maintenance for image-setters feel the invisibility of the infra-red rays as a practical handicap for their work.
For all these reasons some manufacturers of image-setters moved to laserdiodes emitting in the visible red spectral region, and more particularly, to laserdiodes emitting at 670 nm. So the ACCUSET apparatus, marketed by Miles Inc., Agfa division, and the LINO 670 image-setter, marketed by Linotype Co., are equipped with this new type of solid state laser. As a consequence photographic phototype- and image setting materials have to be adapted to this new wavelength of laser emission. More particularly the spectral sensitivity and the absorption spectrum of acutance- and anti-halation dyes should be suitable for 670 nm.
The present invention represents an extension on the teachings on triphenylmethane dyes.
It is a first object of the present invention to provide a new class of light-absorbing dyes showing good absorption at 670 nm.
It is a second object of the present invention to provide photographic red sensitized materials with improved sharpness on exposure at 670.